The present invention relates to a slip-controlled brake system for motor vehicles, comprising at least one static brake circuit into which, in the event of control such as during a controlled braking operation, pressure medium from a dynamic pressure medium circuit is suitably fed through a control valve. The system comprising a brake pressure generator including a master cylinder arrangement and a positioning means which, during the dynamically controlled inflow of pressure medium into the static brake circuit, can be set back against the brake pedal force to thereby maintain the master cylinder piston in a defined position.
Monitoring of slip-controlled brake systems for their proper operation, for safety reasons, is of utmost importance because, in the event of a failure caused by a partial shut-down or a complete cut-off of the control -- depending on the type of error and on the brake system -- it is imperative to nevertheless permit at least an uncontrolled deceleration of the motor vehicle. A defective brake slip control could result in a complete removal of the brake pressure in the wheel brakes which, in the majority of situations, will be more dangerous than locking of one or more of the motor vehicle wheels.
In a conventional monitoring device designed for antilocking brake systems for motor vehicles, the pressure of the servo source is monitored and in the event of a decrease in the said pressure the brake slip control is turned off as soon as a controlled brake operation already initiated has been completed (DE-PS No. 24 11 173).
As the pressure monitoring control is disposed in the supply source, defects in the brake pressure generator affecting the operation of the system cannot be detected despite adequate operating pressure.
Moreover, it is known in the art to detect in a brake system of the afore-mentioned type the hydraulic pressure prevailing at the same time at various points in the interior of the brake pressure generator and to compare the pressure levels with one another in order to include in the monitoring operation both the energy supply system and components of the brake pressure generator (for example, the hydraulic brake force booster) the master valves for the dynamically controlled inflow of pressure medium into the static circuits etc. (DE-OS No. 32 32 052). Upon detection of a defect, the system will be partly shut down in that only the pressure decrease and the dynamic inflow into the static circuits is locked or, depending on the type of defect, the brake slip control will be completely cut off (DE-OS No. 32 32 051). In these prior art brake systems component errors which are not detected by monitoring are likely to occur.
It is, therefore, the object of the present invention to further improve the safety and reliability of a slip-controlled brake system and to develop a system in which errors or defects of individual components heretofore not recognizable can be detected and automatically result in a partial shut-down or cut-off of the brake slip control thereby safeguarding that the motor vehicle can still be decelerated despite the defect occurred and in an effective though uncontrolled manner or by restriction of the control function to some of the wheels.